Method of dissolving thorium values



Patented Mar. 2'7, 195].

UNITED STATES OFFE METHOD OF DISSOLVING THORIUM VALUES No Drawing. Application May 24, 1946, Serial No. 672,172

Claims. (Cl; 23-14.5)

This invention relates to a method of dissolving thorium values. More particularly, this invention relates to a method of dissolving thorium values involving the use of a solvent comprising nitric acid containing a small amount of a fiuorine containing compound.

In this specification and in the claims, the term thorium values is intended to include thorium metal as well as compounds of thorium.

It is known that the bombardment of thorium values with fast neutrons of energies about 2 million electron volts (2 MEV) results in a fission of the thorium. It is also known that the bombardment of thorium values with neutrons having energies of below 1 million electron volts (1 MEV) results not only in the production of Pa and ultimately of U through the prolonged decay of Pa but further that U so produced fundergoes fission by neutrons of such low energies as below 1 million (1 MEV) and even with thermal neutrons. The production of U and/or 19a is thus complicated by the fact that Pa and/or U produced by neutron bombardment may be decomposed by fission under the same bombardment.

In these processes, there are many instances when it becomes necessary to dissolve; thorium values such as metallic thorium, thorium oxide, thorium carbonate and the like. While it is known that thorium values may be dissolved in strong sulfuric acid or aqua regia, the use of such solvents for thorium values may be excessively corrosive on industrial equipment and the rate ofdissolution slow. It is therefore desirable to "develop solvents for thorium values which have no significant corrosive effect upon industrial equipment and which rapidly dissolve the thorium values.

i It is accordingly an object of this invention to provide a method of dissolving thorium values.

, It is a further object of this invention to provide a method of dissolving thorium values involving the use of particular solvents which are less corrosive and more rapid in action than those heretofore known.

Still another object of this invention is the provision of a method of dissolving thorium values which may be conveniently employed in conjunction with methods of preparing U Still another object of this invention is the provision of a solvent for thorium values.

Still another object of this invention is the provision of a solvent for thorium values comprising nitric acid containing a small amount of a fluorine containing compound.

These and other objects of this invention will become apparent to those skilled in the art upon becoming familiar with the following description.

We have found that thorium values such as metallic thorium, thorium oxide; thorium carbonate and the like may be relatively easily dissolved in a solvent comprising nitric acid containing a small amount of certain fluorine containing compounds exemplified by hydrogen fluorile (HF), iiuosilicic acid (HzSiFc), ammonium fiuosilicate ((NH4) 2SiFe) and the like.

In the practice of our invention, the thorium value to be dissolved is immersed in the solvent therefor and heated to a temperature close to -or at the boiling point of the solvent. Generally speaking, in the practice of our invention, the temperature to which the solvent is heated is advantageously between C. to 120 C. In this connection, it has been found that rapid dissolution of thorium values may be obtained at higher temperatures and when utilizing smaller amounts of fluorine containing compound in the solvent. Likewise, with lower temperatures and higher concentrations of fluorine containing compounds, rapid dissolution is eflected. The particular temperatures and concentrations of fluorine containing compounds to be employed will vary depending, among other things, upon the particular thorium values to be dissolved, the type of equipment in which the dissolution is effected and the like. Generally speaking, temperatures of approximately 100 C. and a solvent which is approximately 0.05 M in fluorine containing compounds has been found to be particularly advantageous in effecting rapid dissolution of thorium values without significant corrosion of equipment.

In an advantageous embodiment of our invention, the thorium value is immersed in nitric acid and. the resulting mixture is heated to an elevated temperature such as between C. to 120 C. Upon attaining the elevated temperature,the fluorine containing compound is added and the resulting mixture is maintained at an elevated temperature such as C. until dissolution is complete.

Our invention may be more readily understood by reference to the following specific examples.

Example I 1y dissolved.

lution of the metal observed. The metal was completely dissolved in 30 minutes.

Example II 0.35 e. of thorium was immersedin 5.ml. of concentrated nitric acid in a stainless steel vessel. The vessel was heated to a temperature of 100 C. and the rate of dissolution of the metal was observed. It was found that 30% of the metal was dissolved in 90 minutes;

Example III.

Example I V Example V 0.48 g. of thorium metal. was added to a stainless steel vessel containing 5. ml. concentrated nitric. acid. The contents of the vessel were then heatedto 97 C. and thereaftersuflicient HF was added to make the. SQlVent 0.1 N inI-IF. After addition of the HF thecontentsof thcvessel were heated at 100 C. until the metal was completely dissolved, and the time required fordissolutionofv -the metal afteraddition 'of' the. HE! wasnoted.

At the end of l'l'minute s, themetal was compl'ete Example V] 7 Example VII 0.48 g. of thorium metal-was placed in ml. of concentrated nitric acid contained in a stainless steel vessel. The resulting contents of the vessel were heated to 97 C. whereupon'sufficient HP to render the solvent 0.01 N-inHF was added thereto. Upon addition of the- HF, the contents of the vessel were heated at 100 C. until dissolution of the metal wa s'com'p'lete. The time required for dissolution after the addition of HF wasnoted and found to be. 65 minutes.

Example VIII 0.416 g. of thorium metal was immersed in .10 m

of concentrated nitric acid contained in a stainless steel vessel. The contents of the vessel were heated to 97 C. whereupon the solvent was made 0.01 N in HF. After the addition of HF, the contents of the vessel were heated at 100 C. until the thorium metal was completely dissolved. The time required for complete dissolution was noted and found to be '72 minutes.

Example IX 0.37 g. of thorium metal was immersed in 5 ml. of. concentrated nitric acid contained in a stainless steel vessel. The contents of the vessel were heated to 97 C. whereupon sufficient HzSiFc was added to render the solvent 0.01 N in H2SiFc. Thereafter the contents of the vessel were heated at, 100 C. until all of the metal had dissolved. The, time required for complete dissolution was noted and found to be 20 minutes.

Example X be 21, minutes.

Example XI.

2.15 g. of thorium metal wasimmersedin .7 url. of-a solvent which was 16 N inHNOzand 0.05 N .in HF. The resulting mixture was .heated at 100? C. The time required forcomplete dissolution of the. metal was noted and found to be minutes.

From the. above specific examples, it can be seen that nitricacidcontaining a smallamountof fiuorinecompounds such as. HF. or HaSiFediS: solves thorium metal as rapidlyasHNOs dissolves uranium metal. Generally speaking. rapiddissolution may be effected bythe addition OffSLlf? ficient fluorinecontaining compound; to render theesolvent at least 0.002 M in the compound.

The difierence in solution time betweerrExample X and-ExampleXI results fromv the increaseinweight of metal and decrease in excess acid in the case of the larger sample in Example XL The-following specific examples. are illustra. tive ofthe. application. of our invention to 131164115? solution of compounds of thorium as exemplified by thorium. oxide (ThOz).

Example XII,

0.5 g. of ThOz was placed ina-glass reaction vessel together with 10ml. 8'NHN03. Thecon tents of the vessel were heated to 97 C; whereupon sufiicient HF was added torender'the solvent 0.011 N--in- HF. The mixture was then'heated.

at 100C. until all ofthe oxide-'had dissolv ed. The time between the addition of andth'e complete dissolution of the oxide was recorded and found to be 11 minutes.

. Example XIII assepse Example XIV Examplev XV 0.5 g. ThOz and ml. HNOs were placed in a glass reaction-vessel and heated to 97 C., whereupon sufficient HF was added to the vessel to 'render the'solvent 0.011 N in HF. Thereafter the reaction mixture-was heated at'100 C. until all fof the oxidehaddissolved. The time between the: addition of and complete dissolution of the oxide} was recorded' and found to be 3.5

-- Example XVI- 0.5 g. Th02 and 10 ml. 16 N I-INOawere placed in a glass reaction vessel and heated to 97 C.,

-Thereafter the reaction mixture was heated at 100 C. until all of the oxide had dissolved. The time between the addition of HF and complete dissolution of theoxidewas noted and found to be 3.5 minutes.

Example XVII 0 gf'Ihoz andl'0 ml. lfi N I-INO3 were placed in a glass 'react'ion vessel and heated to 97 C. whereupon the solvent was made 0.0027 N in HF. Thereafter the reac'tionmixturewas heated at 100 C. until all of the oxide had dissolved. The time between the addition of HF and the complete dissolution of the oxide was noted and found to be 5 minutes.

Example XVIII Example XIX 0.5 g. ThO2 and 10 ml. of 8 N HNO3 were placed in a glass reaction vessel and heated to 80 C. whereupon suflicient (NH4)2S1F6 was added to the vessel to render the solvent 0.010 M. in (NI-IUzSiFe. The time between the addition of (NH4) 2SiFs and the complete dissolution of the oxide was recorded and found to be 6 minutes.

Example XX 0.5 g. ThOz and 10 ml. 16 N HNO3 were placed in a glass reaction vessel and heated to 80 C. whereupon sufiicient (NH4)2SiF5 was added to the vessel to render the solvent 0.015 M in (NH4) zSiFe. Thereafter the mixture was heated at 100 C. until all of the oxide had dissolved. The time between the addition of (NH4) zSiFs and the complete dissolution of the oxide was recorded and found to be 9 minutes.

Example XXI 0.5 g. Th0: and 10 ml. 8 N HNOa were placed in a glass reaction vessel and heated to 80 C. whereupon sufficient (NHQaSiFs was added whereupon the solvent was made 0.0055 N in HF.

minutes.

to the mixture to render the solvent 0.002! M in (NH4) 2SiFs. Thereafter the mixture was heated at 100 C. until all of the oxide had dissolved. The time between the addition of (NI-I4) ZSi-Ffi and the complete dissolution of'the'oxide was recorded and found to be 9.5 minutes.

The following three specific examples further illustrate the improvements to be obtained-in the practice of our invention in dissolvingi thorium values over the use of nitric acid without. theaddition of a fluorine containing compound. 0.

v Example XXII v A 10 g. sample of ThOawasheated' in.20 'ml.

' 16 N HNOa (3 times the stoichiometric amount of HNOa required to convert ThOz to the. nitrate) contained in a glass vessel for hours at 100 C. At the end of this timeonly-l .1%,ofjthe..ThOa had dissolved. y Y; n

' Example XXIII I A '10 sampileof the T1102 y din ple XXII was placed in a stainless steel beaker together with 28 ml. 16 N HNOs (3 times the stoichiometric amount of HNO3 required to convert 'IhOz to the nitrate). Sufficient HF was added to render the solvent 0.05 N in HF and the mixture was heated at 105-1l0 C. until all of the ThOz was dissolved. The time required to effect complete dissolution was found to be 20 Example XXIV A' 10 g. sample of the ThOz'employed in ple XXII was placed in a glass vessel together with 28 ml. of 16 N HNOs. .Suflicient=I-IF was added to renderthesolvent 0.05;N-.in HF .and the resulting mixture heated at 100 C. until dissolution of the oxide was complete. The time required for complete dissolution was measured and found to be 50 minutes.

The higher temperature is believed to be chiefly responsible for the shorter solution time resulting from employing the conditions of Example XXIII, although the presence of glass in the conditions of Example XXIV may have tended to increase the solution time.

Example XXV 64 g. pellet of compressed ThOz was placed in a reaction vessel together with 363 ml. of a solvent which was 8 N in HNO; and 0.005 M in (NH4)2SiFs. The mixture was heated for 2 hours at 100 0. Most of the oxide seemed to dissolve in about 10 minutes, while a relatively small amount of it required the total 2 hours before its complete solution.

In the practice of our invention, generally speaking, the amount of nitric acid and the amount of fluorine containing compound will depend upon the size of the sample to be dissolved, the temperatures employed, and the like. However, particularly advantageous results may be generally obtained by utilizing as a solvent a material which is between 8 and 16 N in nitric acid and which is between 0.002 M and 0.5 M in fluorine containing compound. As indicated above, with lower concentrations of fluorine containing compound, generally speaking, higher temperatures are required for dissolution in a reasonable length of time. However, when higher temperatures such as temperatures above C. are employed, corrosion of equipment may result. It is particularly advantageous therefore to operate at temperatures of between 70' C. and 100 C. and when utilizing solvents which are less than 0.2 M in fluorine containing compound, such as 0505 M, and to 13 M in M03.

While our invention has-been particularly described with reference to certain particular embodimentsand with reference to certain specific examples; it is to be understood that the invention is not to be limited thereby. Therefore, changes, omissions and/or additions may be made Without departing from the spirit of the invention as defined in the appended claims which are intended to be limited only as required by the prior art.

We claim:

1=.- A method of dissolving thorium values which comprises heating said thorium values in a solvent containing nitric acid and a small amount of a fluorine containing commune.

2. A method of dissolving thorium values which comprises heating said thorium values in a material containing nitric acid, said material bein up to 0.5 M in a fluorine containing compound.

3. A method of dissolving thorium values which comprises heating said thorium values in the presence of nitric acid containing a small amount of hydrogen fluoride.

4. A method of dissolving thorium values which comprises heating said thorium valueslin the presence of nitric acid containing a small amount of fiuosilicic acid.

5. A method of dissolving thorium values whichcomprisesheating said thorium values in a the presence of nitric acid containing a small amount or ammonium fiuosilicate.

6. A method of dissolving metallic thorium which comprises heating said metallic thorium in the presence or a solvent containing nitric acid and a small amount of a fluorine containing m i'da a. 7. A method of dissolving thorium oxide which comprises heating said oxide in the resen e or a solvent containing a small 'ain'ount'ofa fluorine containingcbmpound;

8. A method or dissolving thorium carbonate which comprises heating said thorium carbonate in the presence of a solvent containing nitric acid and a small amount of a fluorine containing compound 7 I g 9. In a process which includes the step of dis:- solving thorium values, the improvement which comprises contacting said thorium values with solvent containing nitric acid and a small amount of a compound selected are group onsisting of hydrogen fluoride, fiuosilicic acidand ammonium fluosilicate and heating the resulting mixture.

10. A method of dissolving thorium values which comprises immersing said thorium values in a solution which is between 8 and 16 N in nitric acid; rendering said solution between 0.002 and 0.5 N in a fluorine containing compound an heating the resulting mixture to a temperature of between C. and G.

FRANK L; STEAHLY. RAYMOND W. STCJUGH'IGIJ. FEEDER-IO W. SGHULER:

No references. cited. 

1. A METHOD OF DISSOLVING THORIUM VALUES WHICH COMPRISES HEATING SAID THORIUM VALUES IN A SOLVENT CONTAINING NITRIC ACID AND A SMALL AMOUNT OF A FLUORINE CONTAINING COMPOUND. 